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Critical doping in high-Tc superconductors for maximal flux pinning and critical currents

a superconductors and flux pinning technology, applied in the direction of superconductors, superconducting magnets/coils, magnetic bodies, etc., can solve the problems of not ensuring the utility of htsc, high critical current in the presence of magnetic fields, etc., to increase the critical current density of materials and maximize critical current density.

Inactive Publication Date: 2004-08-31
VICTORIA LINK LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

"The invention is about a method for preparing a high temperature superconducting cuprate material to maximize its critical current density (Jc) and to reduce the impact of impurities and grain boundaries on its performance. The method involves controlling the doping state or hole concentration of the material to be higher than the material's maximum superconducting transition temperature (Tc) and about where the normal-state pseudo-gap (E.sub.g) is minimized. The invention also provides a high temperature superconducting cuprate material with a doping state or hole concentration higher than the material's maximum Tc and about where the normal-state pseudo-gap is minimized. The technical effect of the invention is to maximize Jc and to reduce the impact of impurities and grain boundaries on the performance of high temperature superconducting cuprate materials."

Problems solved by technology

For many of these applications such T.sub.c values alone do not guarantee the utility of these HTSC at 77K or higher temperatures.
Even if the grains of the HTSC are crystallographically aligned, otherwise known as textured, and well sintered together, as is commonly achieved in thin-films, such that weak links between the grains are removed, a high critical current in the presence of a magnetic field is not guaranteed.

Method used

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  • Critical doping in high-Tc superconductors for maximal flux pinning and critical currents
  • Critical doping in high-Tc superconductors for maximal flux pinning and critical currents
  • Critical doping in high-Tc superconductors for maximal flux pinning and critical currents

Examples

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example 1

Samples of Y.sub.0.8 Ca.sub.0.2 Ba.sub.2 Cu.sub.3 O.sub.7-.delta. were investigated as a function of oxygen deficiency, .delta., using heat capacity, C.sub.p, and NMR spectroscopy. This HTS material is especially useful because its doping state may be altered from heavily underdoped to heavily overdoped as .delta. is altered from 1 to 0. The hole concentration was determined using the thermoelectric power correlation between Q(290) and p (Tallon et al., U.S. Pat. No. 5,619,141). The values were found to agree well with values determined from the parabolic relationship between T.sub.c and p T.sub.c (p)=T.sub.c,max.multidot. [-82.6 (p-0.16).sup.2 ] and also from estimates of p using bond valence sums from neutron diffraction refinement of atomic coordinates. T.sub.c,max is the maximum in the approximately parabolic hole-concentration dependence of T.sub.c (p). The pseudogap energy, E.sub.g, was determined from fitting the temperature dependence of the entropy and values were confirmed...

example 2

Samples of overdoped Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8+.delta. with different .delta. and underdoped Bi.sub.2 Sr.sub.2 Ca.sub.0.7 Y.sub.0.3 Cu.sub.2 O.sub.8+.delta. with different .delta. were substituted with a range of Co on the Cu site. From the rate of impurity depression of T.sub.c, dT.sub.c / dy, due to the fraction y of Co one may determine the value of the value of .gamma.=C.sub.p / T at T=T.sub.c. Using scaling relations (Tallon, Phys. Rev. B-58, R5956 (1998) one may thence determine E.sub.g and U.sub.o which are plotted in FIG. 2 by the filled symbols. The open triangles are the values of E.sub.g determined for Y.sub.0.8 Ca.sub.0.2 Ba.sub.2 Cu.sub.3 O.sub.7-.delta. from NMR measurements and these show that the two methods give comparable results for E.sub.g. Again one may see that for Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8+.delta., as in Y.sub.0.8 Ca.sub.0.2 Ba.sub.2 Cu.sub.3 O.sub.7-.delta., U.sub.o passes through an unexpectedly sharp maximum in the lightly overdoped regi...

example 3

Samples of Y.sub.0.8 Ca.sub.0.2 Ba.sub.2 Cu.sub.3 O.sub.7.delta. were investigated as a function of oxygen deficiency, .delta., using muon spin relaxation. The muon spin relaxation rate at T=0, .sigma..sub.o, is proportional to .lambda..sub.L.sup.-2. FIG. 3 shows a plot of .lambda..sub.L.sup.-2 as a function of hole concentration, P. .lambda..sub.L.sup.-2. may be seen to pass through a sharp maximum at the critical point p.apprxeq.0.19 where E.sub.g becomes zero. .lambda..sub.L.sup.-2 is a key parameter in determining the magnitude of the irreversibility field. As a consequence critical doping at p.apprxeq.0.19 not only sharply maximises flux pinning but will result in high irreversibility fields.

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Abstract

A method for maximising critical current density (Jc) of high temperature superconducting cuprate materials (HTSC) which comprises controlling the doping state or hole concentration of the materials to be higher than the doping state or hole concentration of the material that provides a maximum superconducting transition temperature (Tc), and to lie at about a value where the normal-state pseudogap reduces to a minimum. Jc is maximised1 at hole concentration p≈0.19. HTSC compounds are also claimed.

Description

The invention comprises a method for preparing a high temperature superconducting cuprate material (HTSC) to maximise the critical current density of the material, in which the doping state or hole concentration of the material is controlled so as to lie at about the point where the normal-state pseudogap reduces to a minimum.Many High-T.sub.c Superconducting Cuprates (HTSC) are known to have superconducting transition temperatures, T.sub.c exceeding the temperature at which liquid nitrogen boils, 77 K. As such they have a potentially large number of applications ranging from power generation, distribution, transformation and control, to high-field magnets, motors, body scanners, telecommunication and electronics. T.sub.c values may be of the order of 93 K for example for YBa.sub.2 Cu.sub.3 O.sub.7-.delta., 95K for example for Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8, 109 K for example for Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10, 120K for example for TlBa.sub.2 Ca.sub.2 Cu.sub.3 O....

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): H01L39/12H10N60/85
CPCH01L39/126Y10S505/742H10N60/857
Inventor TALLON, JEFFERY LEWIS
Owner VICTORIA LINK LTD
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